What I want to do is generate a float between 1.00 to 200.00, let's call this number X. The X determines how much a user "wins", think of it like a multiplier on a casino. The user bets 10$, X is 23.21, the user wins 10*23.21.
If the house and the user should have the same odds (+/- 0) in the long run, the chance of X being, for example, 200.00 should be 1/199 - 1/200. This means Y=1/(X-1) - 1/X where Y = percentage of the chance of X.
The percentage Y should be randomized and I was thinking to do a frand(0, 100, 15). Where:
function frand($min, $max, $decimals = 0)
{
$scale = pow(10, $decimals);
return mt_rand($min * $scale, $max * $scale) / $scale;
}
This means we will know Y, and therefor the next step should be using Y=1/(X-1) - 1/X to determine X. However, I do not know how I can achieve this in PHP. Other ways for the same function:
Y = 1/(X - 1) - 1/X
X^2 - X = 1/Y
X(X - 1) = 1/
So, my question is; how do I solve the X OR is there a better way to achieve what I am trying?
Related
I am trying to figure out if there is a way to find the percentage between 2 numbers.
It's a progress / ranking system.
I want to find the percentage the $current_exp is between the $current_min and the $current_max values, is there a way to achieve this in PHP? So far I've got to this, but it doesn't work as you progress in ranks, it doesn't treat the $current_min as 0 so when you rank up, it says you are like 75% into your next rank progression when you're in fact 0. Does this make sense?
$currentProg = ($current_exp * 100) / $current_max;
Say the current minimum is 18750 and the current maximum is 25100, the current exp is 22000... What percentage from the min to the max is the current exp? This will change each rank as the $current_min and $current_max variables get set depending on the exp of the user.
The next rank is Current min is 25100 Current max is 34230
Currently, when you are at 26000 exp, the output is saying 75.956763073327% which is not correct, it should be like 1 or 2%?
Thanks in advance 🙏
Not a good mathematician, but it looks like it should be:
(Difference of rank - minimum) / (Difference of maximum - minimum) * 100
<?php
$x = 25100;
$z = 34230;
$y = 26000;
echo ($y - $x + 1) / ($z - $x + 1) * 100; // outputs 9.8674843938232 %
Online Demo
Note: + 1 is added to both numerator and denominator to avoid divide by zero errors.
How do I calculate the percentage of increase or decrease of two numbers in PHP?
For example: (increase)100, (decrease)1 = -99%
(increase)1, (decrease)100 = +99%
Before anything else you need to have a solid understanding of the meaning of percentages and how they are computed.
The meaning of "x is 15% of y" is:
x = (15 * y) / 100
The arithmetic operations with percentages are similar. If a increases with 12% (of its current value) then:
a = a + (12 * a) / 10
Which is the same as:
a = 112 * a / 100
Subtracting 9% (of its current value) from b is:
b = b - (9 * b) / 100
or
b = b * 91 / 100
which actually is 91% of the value of b (100% - 9% of b).
Turn the above a, b, x, y into PHP variables (by placing $ in front of them), terminate the statements with semicolons (;) and you get valid PHP code that performs percentage operations.
PHP doesn't provide any particular function that helps working with percentages. As you can see above, there is no need for them.
My 2 cents ;)
Using PHP
function pctDiff($x1, $x2) {
$diff = ($x2 - $x1) / $x1;
return round($diff * 100, 2);
}
Usage:
$oldValue = 1000;
$newValue = 203.5;
$diff = pctDiff($oldValue, $newValue);
echo pctDiff($oldValue, $newValue) . '%'; // -79.65%
Using Swift 3
func pctDiff(x1: CGFloat, x2: CGFloat) -> Double {
let diff = (x2 - x1) / x1
return Double(round(100 * (diff * 100)) / 100)
}
let oldValue: CGFloat = 1000
let newValue: CGFloat = 203.5
print("\(pctDiff(x1: oldValue, x2: newValue))%") // -79.65%
I need to create a business logic or php function to compute the following: given some input $rank (which is the alexa ranking) I need to compute some $points in such a way that $points will be high for the top ranking website and will decrease with increasing $rank value.
I imagine something like this:
function($rank)
{
$points = x*$rank;
return $points;
}
How do I get $points in such a way that
if the rank is 1 then the points returned is maximum (e.g. 10000).
if rank is 2 then $points returned will be 9500 or nearby.
if rank is 4 then $points returned will be 6000 or nearby.
if rank is 200 $points returned will be 2 or whatever the function will return.
Rule: if $rank is less then $points should be more. Maximal value of $points is 10000 which is for $rank=1.
Now as the $rank increases the $points value should decrease accordingly.
There are many formulas which might satisfy your requiremements.
Nested powers
One possibility:
$points = 10000 * pow(0.993575964272119, pow($rank, 3.16332422407427) - 1)
This gives you the following results:
f(1) = 10000
f(2) = 9500
f(4) = 6000
f(9) = 12.065
f(10) = 0.84341
f(200) = 0
So the three values you fixed (1, 2 and 4) are all satisfied, but the result for 200 indicates that this might not be exactly what you're looking for. The curve looks like this:
By the way, I found this using python and mpmath, by fixing the form of the formula and determining the numbers with the many digits numerically:
>>> import mpmath
>>> print(mpmath.findroot((lambda a,b: 10000*a**(2**b - 1) - 9500,
... lambda a,b: 10000*a**(4**b - 1) - 6000),
... (0.995, 2.7)))
[0.993575964272119]
[ 3.16332422407427]
If you decide on a different form of the function, this approach might be adapted.
Exp of a polynomial
A possible different form with the desired properties would be this:
$points = exp(9.14265175282929 + $rank*(0.127179575914116 - $rank*0.0594909567672230))
This does not decrease quite as quickly as the one above:
f( 1) = 10000
f( 2) = 9500
f( 4) = 6000
f( 13) = 2.1002
f( 14) = 0.47852
f(200) = 0
It was obtained by solving this system of equations:
a + b + c = log(10000)
a + 2b + 4c = log( 9500)
a + 4b + 16c = log( 6000)
to obtain the coefficients a through c for the polynomial. One can add another degree to match f(200)=2 as well, but in that case, the last coefficient will become positive, which means that points will start to increase with rank for very large ranks.
If you want to match that f(200)=2 as well, you can do so using
$points = exp(max(8.86291000469285 - $rank*0.0408488141206645,
9.14265175282929 + $rank*(0.127179575914116 - $rank*0.0594909567672230)))
although this will result in a bend in your curve.
To compare these alternatives to the above:
function getPoints($rank)
{
$returnValue = -0.005 * $rank * $rank - 0.035 * $rank + 100.040;
if ($returnValue < 0) $returnValue = 0;
return $returnValue;
}
This was my thinking.
Function is not forking for large values:
it should atleast give some small value for large ranks...
like if rank is 2000000 then points will be 2.
Thnx btw
Wow, this one is though!
I'm trying to find in PHP the % of a value relative to the Y axis. If we refer to this graph : http://en.wikipedia.org/wiki/Semi-log_graph (2009 outbreak of influenza A), let's say that I want to find what % is a value "256" on the chart.
Visually, it's easy : it's a bit more than a 1/3 or 33%. If we look at the 1024 value, it's around 50% of the height of the Y axis. 131072 would be 100%.
So how do I calculate this with PHP?
Let's take this graph and take X = day 0 and Y = 256. What is 256 as a % of Y ?
Thanks a lot to anyone can compute this baby :)
percent = 100 * ( log(y) - log(y1) ) / ( log(y2) - log(y1) )
where
y = value
y1 = smallest value in y-axis
y2 = largest value in y-axis.
when y1 = 1.0 then you can simplify the other answers given here (since log(1)=0 by definition)
percent = 100 * log(y)/log(y2)
Note that not all log charts have 1.0 as the lowest value.
ln(131072) = 11.783 is 100%
ln(1024) = 6.931 is 58.824%
in PHP, that function is called log()
no need to set the base, as you are dividing them to find the relative value.
Alex got it, but to generalize for you and PHPize
logPercent = log(x) / log(top) * 100;
If you take the log of your max y value (131072 in your case) and the log of your y value (256), you end up with a height and a y value which is linear in relation to your drawn axis. you can divide them to get a decimal of the height and times by 100 for %:
using log base 2 seen as it gives integers (though any base should be fine).
log(256) / log(131072) = 8/17 = 0.47 = 47%
in php:
(log(256, 2) / log(131072, 2))*100;
I want to add a number to a var. This number should be bigger when var is small and smaller when var is big. I have calculate the optimum values: when var=1, function should add 125. When var=50 function should add 420. I was thinking about sin function, but I have no idea how to "personalize" this function to work with it. (I am using php)
For a function with the form:
f[x_] := x + Sin[y*x + z]
Subject to the constraints
f[1] == 1 + 125 && f[50] == 50 + 420
You have
{{y -> 1/49 (-ArcSin[125] + ArcSin[420]),
z -> 1/49 (50 ArcSin[125] - ArcSin[420])}}
which is approximately
{{y -> 0. - 0.0247338 I, z -> 1.5708 - 5.49671 I}}
Between 0 and 70, this gives:
An approximate function, using only real values, is:
f(x) = x + 121.94629730754633 cosh(0.02473378688005212 x) +
121.94219707312345 sinh(0.02473378688005212 x)
The sine function is periodic and probably not suitable for the task.
Your example is not clear: you say add 'bigger number when var is small and smaller number when var is bigger', but add 125 to 1 and 420 to 50, which contradicts the text.
One possibility is the reciprocal function - it meets your stated requirements but not your example requirements.
Given just 2 data points, we can deduce a linear relationship:
y = 125 + (420 - 125) / (50 - 1) * (x - 1)
which is approximately:
y = 119 + 6x
Check:
x = 1; y = 125
x = 50; y = 419
The approximate factor 6 is a rounding of 6.0204081632 ... which is an intriguing sequence in the fractional part.
Try to make a linear equation projection.
VarAdd = Var*Slop+Start; eq [1]
125=1*Slop+Start ---1
420=50*Slop+Start –2
Solve Slop and Start then apply eq[1] any time.